In a projection type display apparatus, making the contrast higher and making the brightness higher are requested. More light can be taken in as the F values of an illumination optical system and an imaging optical system are smaller so that it tends to be more advantageous in making the brightness higher. On the other hand, a liquid crystal display device and a polarization device such as a polarization beam splitter have incidence angle dependencies respectively so that a displayed image with a higher contrast can be obtained as the incidence angle of a ray of light is smaller, that is, as the F values of an illumination optical system and an imaging optical system are greater.
Accordingly, a projection type display apparatus has been proposed which is designed so that a user can adjust a balance between the contrast and the brightness of a displayed image in accordance with the brightness of use environments. Patent documents 1 disclose that at least one of an illumination optical system and a projection lens is provided with a diaphragm. In addition, the point that two diaphragms are made to interlock is mentioned. Furthermore, patent documents 2 disclose an example in which shading is done by diaphragms provided in an illumination optical system and a projection lens, and disclose an example in which the diaphragm shapes of the diaphragms provided in the illumination optical system and the projection lens are similar figures.